Update README.md

[eliotwrobson]

Minor readme changes as requested here: openjournals/joss-reviews#5759 (comment)

Going to wait for approval by @Viech before merging to cut down on the number of changes.

[coveralls]

coverage: 99.847%. remained the same when pulling f0d6110 on eliotwrobson:readme_changes into a4396b7 on caleb531:develop.

[Viech]

• grammar fix: researchers that wishing to → researchers that wish to / researchers looking to
• I also think the comma before and in the last sentence may be wrong; not sure.
• just a suggesion: for users in educational contexts → for instructors teaching courses on theoretical computer science / on automata theory is a bit more specific

Otheriwse LGTM!